* [PATCH] sg: Fix double-free when drives detach during SG_IO
@ 2015-10-30 23:57 Calvin Owens
2015-11-02 20:57 ` Douglas Gilbert
0 siblings, 1 reply; 3+ messages in thread
From: Calvin Owens @ 2015-10-30 23:57 UTC (permalink / raw)
To: Doug Gilbert, James E.J. Bottomley
Cc: linux-scsi, linux-kernel, kernel-team, calvinowens
In sg_common_write(), we free the block request and return -ENODEV if
the device is detached in the middle of the SG_IO ioctl().
Unfortunately, sg_finish_rem_req() also tries to free srp->rq, so we
end up freeing rq->cmd in the already free rq object, and then free
the object itself out from under the current user.
This ends up corrupting random memory via the list_head on the rq
object. The most common crash trace I saw is this:
------------[ cut here ]------------
kernel BUG at block/blk-core.c:1420!
Call Trace:
[<ffffffff81281eab>] blk_put_request+0x5b/0x80
[<ffffffffa0069e5b>] sg_finish_rem_req+0x6b/0x120 [sg]
[<ffffffffa006bcb9>] sg_common_write.isra.14+0x459/0x5a0 [sg]
[<ffffffff8125b328>] ? selinux_file_alloc_security+0x48/0x70
[<ffffffffa006bf95>] sg_new_write.isra.17+0x195/0x2d0 [sg]
[<ffffffffa006cef4>] sg_ioctl+0x644/0xdb0 [sg]
[<ffffffff81170f80>] do_vfs_ioctl+0x90/0x520
[<ffffffff81258967>] ? file_has_perm+0x97/0xb0
[<ffffffff811714a1>] SyS_ioctl+0x91/0xb0
[<ffffffff81602afb>] tracesys+0xdd/0xe2
RIP [<ffffffff81281e04>] __blk_put_request+0x154/0x1a0
The solution is straightforward: just set srp->rq to NULL in the
failure branch so that sg_finish_rem_req() doesn't attempt to re-free
it.
Additionally, since sg_rq_end_io() will never be called on the object
when this happens, we need to free memory backing ->cmd if it isn't
embedded in the object itself.
KASAN was extremely helpful in finding the root cause of this bug.
Signed-off-by: Calvin Owens <calvinowens@fb.com>
---
drivers/scsi/sg.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 9d7b7db..503ab8b 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -787,8 +787,14 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
return k; /* probably out of space --> ENOMEM */
}
if (atomic_read(&sdp->detaching)) {
- if (srp->bio)
+ if (srp->bio) {
+ if (srp->rq->cmd != srp->rq->__cmd)
+ kfree(srp->rq->cmd);
+
blk_end_request_all(srp->rq, -EIO);
+ srp->rq = NULL;
+ }
+
sg_finish_rem_req(srp);
return -ENODEV;
}
--
2.5.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] sg: Fix double-free when drives detach during SG_IO
2015-10-30 23:57 [PATCH] sg: Fix double-free when drives detach during SG_IO Calvin Owens
@ 2015-11-02 20:57 ` Douglas Gilbert
2015-11-03 4:52 ` Martin K. Petersen
0 siblings, 1 reply; 3+ messages in thread
From: Douglas Gilbert @ 2015-11-02 20:57 UTC (permalink / raw)
To: Calvin Owens, James E.J. Bottomley; +Cc: linux-scsi, linux-kernel, kernel-team
On 15-10-31 12:57 AM, Calvin Owens wrote:
> In sg_common_write(), we free the block request and return -ENODEV if
> the device is detached in the middle of the SG_IO ioctl().
>
> Unfortunately, sg_finish_rem_req() also tries to free srp->rq, so we
> end up freeing rq->cmd in the already free rq object, and then free
> the object itself out from under the current user.
>
> This ends up corrupting random memory via the list_head on the rq
> object. The most common crash trace I saw is this:
>
> ------------[ cut here ]------------
> kernel BUG at block/blk-core.c:1420!
> Call Trace:
> [<ffffffff81281eab>] blk_put_request+0x5b/0x80
> [<ffffffffa0069e5b>] sg_finish_rem_req+0x6b/0x120 [sg]
> [<ffffffffa006bcb9>] sg_common_write.isra.14+0x459/0x5a0 [sg]
> [<ffffffff8125b328>] ? selinux_file_alloc_security+0x48/0x70
> [<ffffffffa006bf95>] sg_new_write.isra.17+0x195/0x2d0 [sg]
> [<ffffffffa006cef4>] sg_ioctl+0x644/0xdb0 [sg]
> [<ffffffff81170f80>] do_vfs_ioctl+0x90/0x520
> [<ffffffff81258967>] ? file_has_perm+0x97/0xb0
> [<ffffffff811714a1>] SyS_ioctl+0x91/0xb0
> [<ffffffff81602afb>] tracesys+0xdd/0xe2
> RIP [<ffffffff81281e04>] __blk_put_request+0x154/0x1a0
>
> The solution is straightforward: just set srp->rq to NULL in the
> failure branch so that sg_finish_rem_req() doesn't attempt to re-free
> it.
>
> Additionally, since sg_rq_end_io() will never be called on the object
> when this happens, we need to free memory backing ->cmd if it isn't
> embedded in the object itself.
>
> KASAN was extremely helpful in finding the root cause of this bug.
>
> Signed-off-by: Calvin Owens <calvinowens@fb.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Thanks.
> ---
> drivers/scsi/sg.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 9d7b7db..503ab8b 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -787,8 +787,14 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
> return k; /* probably out of space --> ENOMEM */
> }
> if (atomic_read(&sdp->detaching)) {
> - if (srp->bio)
> + if (srp->bio) {
> + if (srp->rq->cmd != srp->rq->__cmd)
> + kfree(srp->rq->cmd);
> +
> blk_end_request_all(srp->rq, -EIO);
> + srp->rq = NULL;
> + }
> +
> sg_finish_rem_req(srp);
> return -ENODEV;
> }
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] sg: Fix double-free when drives detach during SG_IO
2015-11-02 20:57 ` Douglas Gilbert
@ 2015-11-03 4:52 ` Martin K. Petersen
0 siblings, 0 replies; 3+ messages in thread
From: Martin K. Petersen @ 2015-11-03 4:52 UTC (permalink / raw)
To: Douglas Gilbert
Cc: Calvin Owens, James E.J. Bottomley, linux-scsi, linux-kernel,
kernel-team
>>>>> "Doug" == Douglas Gilbert <dgilbert@interlog.com> writes:
>> In sg_common_write(), we free the block request and return -ENODEV if
>> the device is detached in the middle of the SG_IO ioctl().
>>
>> Unfortunately, sg_finish_rem_req() also tries to free srp->rq, so we
>> end up freeing rq->cmd in the already free rq object, and then free
>> the object itself out from under the current user.
>>
>> This ends up corrupting random memory via the list_head on the rq
>> object. The most common crash trace I saw is this:
>> Signed-off-by: Calvin Owens <calvinowens@fb.com>
Doug> Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Applied.
--
Martin K. Petersen Oracle Linux Engineering
^ permalink raw reply [flat|nested] 3+ messages in thread
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2015-11-02 20:57 ` Douglas Gilbert
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